A system that performs data management by distributing data into a plurality of disk units for data redundancy such as RAID (Redundant Array of Inexpensive Disks) is well-known. In the RAID system, power supply units for supplying a power to the disk units often have a redundant configuration so as to enhance reliability of the data management. For instance, two power supply units are disposed in the RAID system. Therefore, when one of the power supply units detects an abnormality and stops a voltage output, the other power supply unit supplies the voltage so that a sufficient power supply capacity in the RAID system is obtained. Japanese Laid-open Patent Publication No. 2008-113499 and Japanese National Publication of International Patent Application No. 2006-528479 are examples of conventional technique.
For instance, in the case that two voltages of +12V and +5V are supplied to the disk units, when the abnormality occurs in a voltage generation function of one of the power supply units and the voltage output stops, one of the power supply units in which the abnormality occurs is separated from the RAID system. Under this condition, when the abnormality occurs in the other power supply unit, it is separated similarly from the system as a voltage abnormality. As a result, it becomes impossible to supply the voltage to the disk units. In this case, a maintenance person is dispatched. The abnormality of the power supply unit in the RAID system is described above, however there is a similar problem also in another system that has a redundancy configuration.